I think you're over reacting to be honest. I don't think it's incompetent. Missing an opportunity? Yes, sure. But I'm sure risk vs reward was weighed. Not to mention the OEM harness does not play nicely with four pin US trailer harnesses.
As for install difficulty, etrailer.com lists the V60 hitches as 10/10. That's crazy as the most difficult bit is pulling the bumper - but that's more a leap of faith you won't break anything than difficult. It was easy and done in 60min. My other car is rated 5/10 yet you have to drill four holes into the subframe and fish wires so I'm not sure how their rating system works.
All in all, this is my first Volvo (or lux car) and it's interesting to me how reliant everyone on the forum is for OEM parts for everything - from wheels to trailer hitches. Why bellyache when the Curt (and other mfr) hitch works and has been proven by your fellow Swedespeeders? Same now that at least two people have tried the wiring harness. All in I was under $160 for both and they work - towing and hitch bike racks. Yes, my parking sensors don't automatically turn off when a trailed harness is plugged in but I can manage pushing that button - even multiple times on a journey. Your warranty will not be voided for an aftermarket hitch.